Cactus
Cacti can be found in the desert regions. Occasionally they will grow a prickly pear.
Climbing on a cactus will reduce the Health of a Blockhead and cause them to make an "Ow" sound of pain. Placing ladders over the cactus does not prevent this.
Planting a prickly pear in sand or compost will spawn a cactus.
Harvesting a block of cactus will produce a stick, and using a machete will produce three. This makes cacti effectively an all-leaf tree.
When a cactus dies, it will turn black and begin despawning from the top down. There have been no reports of anything being left behind.